EOR polymer for high temperature and high salinity oilfield

—The molecular design, synthesis and performance evaluation

Polymer flooding is the most common and effective means in EOR, but there is no suitable polymers for high temperature and high salinity reserviors

There is large amount of reserves in high temperature and high salinity reserviors in Sinopec which are suitable for polymer flooding but now the recovery ratio is low.

To resolve the water problems resulted from polymer flooding.

The basic requirements of the EOR polymer：completely dissolved in high salt

solution is less than 2 h, high apparent viscosity at high temperature and

good thermal stability

Ways to improve the polymer properties

The most commonly used method：

1.Increasing the molecular weight of polymers——Couldn’t improve the performance of temperature and salt resistance

2.Increasing the ratio of temperature and salt resistance monomer——

Will decrease the molecular weight and the solution apparent viscosity of the polymers

3.Introducing hydrophobic monomers to improve the interactions between molecular chains and then increase the solution apparent viscosity——will increase the earth absorption

4. 1+2，Increasing the ratio of temperature and salt resistance monomer and increasing the molecular weight——Difficult to achieve by the existing polymerization technology

Is there any possibility by changing the molecular microstructure to improve the polymers?

The significance of control the molecular microstructure

Means to get micro-block PAM——Template polymerization

Simple, moderate, environment-friendly, easy to operate

By using AMPS to increase the temperature and salt resistance ability of polymer

The introduce of AMPS decreased the hydrolysis rate of the molecular chains,

on the other hand it reduced the effect of Ca2+ and Mg2+ ions on the molecular

main chains, which could increase the tolerance of the polymer to the temperature

and salt.

Template polymerization of AM and AA

The template PDMC has strong interactions with ionized AA through

electrostatic interaction while has no interactions with AM.

The effect of template PDMC on the polymerization reaction rate

The reaction rate increased as the concentration of PDMC increased and reached the maxim at [PDMC]/[AA]=1.2 and then decreased which met the template polymerization mechanism I.

The template PDMC will significantly change the microstructure of the product.

The effect of PDMC on the reactivity ratio

Determined by Kelen-Tudos

The presence of PDMC significantly promoted the reactivity ratio of AM and AA especially AA’s , the reactivity ratio was greater than 1 which indicated that micro-block structure would be formed in the product.

2. The apparent viscosity of the polymer solution(The decrease of molecular weight caused by the introduction of temperature and salt resistance monomers which reduced the apparent viscosity of the polymer solution) ——template polymerization

3. Solubility ——adjust the prescription and introduce some additives

The process of the polymerization

The typical increase of temperature with time

The polymerization was initiated at low temperature and polymerized in a adiabatic reactor.

LH-2500 has no hydrophobically associating behavior in aqueous solution

The order of the apparent viscosity of the solution at 1500mg/L and 85 ℃ is

LH-2500>hydrophobically associating PAM ＞ MO-4000

The simulated adsorption of the polymer by the earth at 25℃

The apparent viscosity of LH-2500 and MO-4000 has no change during the experiment while the hydrophobically associating PAM decreased rapidly which indicated that LH-2500 has no visible adsorption on the earth

Thermal stability

LH-2500 has higher thermal stability, could achieve the requirement of enhanced oil recovery

Compared with other temperature and salt resistance polymers used in Sinopec Shengli oilfield

The apparent viscosity performance of LH-2500 was better than all the polymers

currently in use, even increase the concentration by 20% of other polymers.

Summary of the characteristics of this LH-2500

LH-2500 has no hydrophobically associating behavior in aqueous solution, so the

adsorption by the earth was not obvious.

LH-2500 could be dissolved in oilfield produced water directly and the completely

dissolved time is less than two hours.

The performance of the solution viscosity and thermal stability was very good.

LH-2500 was the best temperature and salt resistance EOR polymer material up till now, it could fulfill the requirement of oilfield with high temperature (＞80 ℃) and high salt.

the permeability of each tube is different to simulate the diversity of the reservoir.

Tube：L：60 cm，D：3.8 cm，A：11.3 cm2，V：680 ml

Filled sand：the produced sand of Shengli oilfield

Permeability of hypertonic tube：～2500mdc

Permeability of hypotonic tube ：～400mdc

Pressure measurement points：a total pressure measurement point ahead the

tubes and two pressure measurement points along each tube

Temperature：85℃

The viscosity of the crude oil：85℃，60mPa.s

The concentration of PAM：1.5g/L solved in the simulated Shengli oilfield

produced water

The injection volume of PAM：0.4PV

The injection rate：0.5ml/min

Without the presence of surfactant only PAM

The apparent viscosity of the PAM solution

The changing of the pressure at each pressure measurement point

The pressure increased more significantly after the injection of LH-2500 than the injection of

MO-4000, after changing to inject the water, the residual pressure is much higher, which indicated that LH-2500 has higher core drag coefficient and residual drag coefficient.

The effect of inject volume (PV) on the recovery ratio

After the injection of PAM and changing to water, the recovery ratio of the two tubes

both increased significantly

The result of the recovery—— MO-4000

The result of the recovery—— LH-2500

Even though the recovery ratio is higher in the process of water flooding, the average recovery ratio of LH-2500 is still much higher than that of MO-4000.

The enhanced recovery by LH-2500+PS

LH-2500 and petroleum sulfonate have a good synergy, the recovery ratio of hypertonic tube was promoted up to 50%.

The permeability of the tubes are changed to about 1000mdc and 5000mdc

Increase the permeability, the recovery ratio of the two tubes decreased slightly, especially the hypotonic tube, but the recovery ratio of the hypertonic tube was still significantly higher than that of the one used PAM alone.

Summary of the simulated enhanced oil recovery

Compared with MO-4000, LH-2500 has higher core resistance efficiency and

residual resistance efficiency which indicated that LH-2500 has the ability to

promote the sweep efficiency and the sweep range.

For the recovery ratio of the hypertonic tube LH-2500 and MO-4000 was almost

the same, but in the hypotonic tube the recovery ratio of LH-2500 was much

higher than that of MO-4000 due to the higher ability to increase the sweep